Conventional electromagnetic light reflectors consist of flexible members that move relative to an incident light beam to reflect light at a predetermined angle. For magnetically based devices, the movement of the reflectors is usually due to interactions of energized coils with permanent magnets arranged in close proximity to one another. For electrostatically based devices the movement of the reflectors is usually due to the interactions of the charged electrodes arranged proximate to one another.
Texas Instruments produces a Digital Micromirror Device.TM. (DMD) wherein each DMD pixel is monolithically integrated MEMS (microelectromechanical systems) superstructure cell fabricated over a CMOS SRAM cell. Plasma etching a sacrificial layer develops air gaps between the metal layers of the superstructure of the silicon chip. The air gaps free the structure to rotate about two compliant torsion hinges. The mirror is connected to an underlying yoke which in turn is suspended by two thin torsion hinges to support posts. The yoke is electrostatically attracted to the underlying yoke address electrodes. The mirror is electrostatically attracted to mirror address electrodes. The mirror and yoke rotate until the yoke comes to rest against mechanical stops that are at the same potential as the yoke.
Micro-engineering (MEMS) is a rapidly growing field which is impacting many applications today. Micro-engineered devices and systems involving silicon planar technology can be mass produced with features from one to a few hundred microns having tolerances in micron or submicron level. Most of the current micro-engineering technologies are evolved from the adaptation of thin films, photolithographic and etching technologies generally applied to silicon wafers on which silicon monoxide, silicon dioxide, silicon nitride and the like thin films are deposited and etched thereafter yielding planar configuration. Although the planar silicon technology is capable of building a three dimensional array, the process steps involved in building those structures are many and very often exceed 20 to 30 steps thus making the process less attractive for many applications. Furthermore, there are many complicated structures which are not possible to be incorporated in the silicon planar technology because of certain limitations of the thin film technology.
Although micromolding ceramic reflectors can be automated and made cost-effectively, incorporation of electronic circuitry on ceramic substrates are not that cost effective as silicon technology.
The current planar technologies using silicon substrates are inadequate for the fabrication of an integrated and self-contained three dimensional arrays of micro-devices such as microreflectors which can be used for displaying images. Thin film technology along with etching processes which are used to build three dimensional structures on a silicon wafer have many limitations. One of the greatest drawbacks of the silicon technology is that it is not possible to build a buried helical coil or a uniform vertical cylindrical column having higher length to radius aspect ratio, and similar complex configurations. Furthermore, building three dimensional multilayered structures using thin film technology involves multiple process steps and therefore makes this process not economically feasible.